In recent years, a technology called OpenFlow has been proposed (refer to Patent Literature 1 and Non Patent Literatures 1 and 2). OpenFlow treats communication as an end-to-end flow, and performs path control, failure recovery, load balancing, and optimization for each flow. An OpenFlow switch, the specification of which is defined in Non Patent Literature 2, comprises a secure channel for communicating with an OpenFlow controller functioning as a control device, and operates according to a flow table suitably added or rewritten by the OpenFlow controller. In the flow table, a set of matching rules (header field) matched against a packet header, flow statistic information (Counters), and an action (Actions) defining the contents of processing is defined for each flow (refer to FIG. 19).
A communication system 1 using the OpenFlow technology can be constituted by, for instance, a controller 114 corresponding to the OpenFlow controller and OpenFlow switches (referred to as “OFS” hereinafter) 121 to 123, and 131 to 133 as shown in FIG. 20.
For instance, when a communication terminal 140 starts to communicate with a communication terminal 142, the system operates as shown in FIG. 21. Upon receiving a packet sent by the communication terminal 140, the OFS 121 searches an entry having matching rules compatible with the header information of the received packet in a flow table. If no entry matching the received packet is found as a result of the search, the OFS 121 sends a new flow detection notification (Packet-In) message equipped with information about the received packet to the controller 114 via a secure channel after buffering the received packet, and requests the controller 114 to determine the path of the packet based on the sender and the receiver of the received packet. The controller 114 specifies the communication terminal 142 as the destination of the packet from the information of the new flow detection notification, sends a flow entry (processing rule) setting (FlowMod) message to set a flow entry realizing communication between the communication terminal 140 and the communication terminal 142 in the OFSs on the path. The OFS 121 forwards the buffered packet using the entry stored in the flow table as a processing rule. A subsequent packet flow is forwarded without requesting the controller 114 to determine the path since the corresponding entry already exists.
Further, Patent Literature 2 discloses a method for configuring a hierarchical network recognizing connection states between devices constituting the network as a hierarchical structure and based on topology information including hierarchy information. Patent Literature 2 states that a server managing each layer or an information relay device having functions of a server determines identification information usable by downstream relay devices connected to the server or the information replay device through an interface on the downstream side of the server or the information relay device, and informs the determined identification information to the downstream relay devices so as to realize effective address distribution in the hierarchical network configuration.